Theopisthokonts (fromAncient Greekὀπίσθιος (opísthios) 'rear, posterior' andκοντός (kontós) 'pole, i.e.flagellum') are a broad group ofeukaryotes, including both theanimal andfunguskingdoms.^[5] The opisthokonts, previously called the "Fungi/Metazoa group",^[6] are generally recognized as aclade. Opisthokonts together withApusomonadida andBreviata comprise the larger cladeObazoa.^{[7][8][9][10][11]}

Opisthokont Temporal range:1010–0 Ma[1] Pha. Proterozoic Archean Had.
Clockwise, from top left:Abeoforma whisleri (Mesomycetozoea);Amanita muscaria (Fungi);Desmarella moniliformis (Choanoflagellatea);bonnet macaque (Metazoa);Nuclearia thermophila (Nucleariida);Ministeria vibrans (Filasterea)
Scientific classification
Domain:	Eukaryota
Clade:	Amorphea
Clade:	Obazoa
Clade:	Opisthokonta Copeland 1956,[2]emend.Cavalier-Smith 1987,[3]emend. Adlet al., 2005[4]
Subgroups
Holomycota Holozoa

A common characteristic of opisthokonts is thatflagellate cells, such as thesperm of most animals and thespores of thechytridfungi, propel themselves with a singleposterior flagellum. It is this feature that gives the group its name. In contrast, flagellate cells in other eukaryote groups propel themselves withone or moreanterior flagella. Flagellate cells however have been secondarily lost in some opisthokont groups, including most of the fungi.^[7]

Opisthokont characteristics include synthesis of extracellularchitin in exoskeleton, cyst/spore wall, or cell wall of filamentous growth and hyphae; the extracellular digestion of substrates with osmotrophic absorption of nutrients; and other cell biosynthetic and metabolic pathways. Genera at the base of each clade are amoeboid andphagotrophic.^[12]

The close relationship between animals and fungi was suggested byThomas Cavalier-Smith in 1987,^[3] who used the informal name opisthokonta (the formal name has been used for thechytrids byCopeland in 1956), and was supported by later genetic studies.^[13]

Early phylogenies placed fungi near theplants and other groups that havemitochondria with flatcristae, but this character varies. More recently, it has been said that holozoa (animals) and holomycota (fungi) are much more closely related to each other than either is to plants, because opisthokonts have a triple fusion ofcarbamoyl phosphate synthetase,dihydroorotase, andaspartate carbamoyltransferase that is not present in plants, and plants have a fusion ofthymidylate synthase anddihydrofolate reductase not present in the opisthokonts. Animals and fungi are also more closely related to amoebas than to plants, and plants are more closely related to theSAR supergroup of protists than to animals or fungi.^{[citation needed]} Animals and fungi are bothheterotrophs, unlike plants, and while most fungi aresessile like plants, there are also sessile animals.

Cavalier-Smith and Stechmann argue that the uniciliate eukaryotes such as opisthokonts andAmoebozoa, collectively calledunikonts, split off from the otherbiciliate eukaryotes, calledbikonts, shortly after theyevolved.^[14]

Opisthokonts are divided intoHolomycota or Nucletmycea (fungi and all organisms more closely related to fungi than to animals) andHolozoa (animals and all organisms more closely related to animals than to fungi); no opisthokonts basal to the Holomycota/Holozoa split have yet been identified.^{[citation needed]} The Opisthokonts was largely resolved by Torriella et al.^[15] Holomycota and Holozoa are composed of the following groups.^{[citation needed]}

• Holomycota (Fungus-like)
  • Fungi
    • Includes:
      • chytrids (flagellated,zoosporic fungi)
      • Fonticula^[16] (more recent work considers this to be part ofCristidiscoidea, a sister group to the fungi)
      • Hyaloraphidium (previously thought to be agreen alga, now considered a fungus)
      • microsporidia (previously thought to beapicomplexia)
      • Nucleariida (more recent work considers this to be part ofCristidiscoidea, a sister group to the fungi)
    • Excludes:
      • labyrinthulomycetes (slime nets) (now included in theSAR supergroup)
      • myxomycetes (now included inamoebozoans)
      • oomycetes (water molds) (now included in theSAR supergroup)
  • Rozellida (placement uncertain)
• Holozoa (Animal-like)
  • Corallochytrium (formerly considered aHeterokont)
  • Filozoa
    • Animalia (includingmyxozoa)
    • Choanoflagellata (flagellates formerly included in protozoa)
    • Filasterea
  • Mesomycetozoea
    • Amoebidiales (formerly considered trichomycetes)
    • Dermocystida (formerly considered parasitic fungi or sporozoans)
    • Eccrinales (formerly considered fungi)
    • Ichthyophonida (formerly considered parasitic fungiincertae sedis)

The followingphylogenetic tree indicates the evolutionary relationships between the different opisthokont lineages, and the time divergence of the clades in millions of years ago (Mya).^[17][18][19]

•  
  Nuclearia (Nucleariida)
•  
  Rozella sp. (Rozellida)
•  
  Microsporidian spore (Microsporidia)
•  
  Chytrid (flagellated fungus)
•  
  Sphaeroforma sp. (Mesomycetozoea)
•  
  Ministeria sp. (Filasterea)
•  
  Capsaspora sp. (Filasterea)
•  
  Salpingoeca (Choanoflagellatea)
•  
  Desmarella sp. colony (Choanoflagellatea)
•  
  Two opisthokonts: a human (Metazoa) and a mushroom (Fungi)

• Tree of Life Eukaryotes